Outphasing-calibration in a radio frequency (RF) transmitter device

ABSTRACT

In an outphasing radio frequency (RF) transmitter, detecting differences of a first plurality of signal characteristics of a first plurality of amplified RF signals across at least a transmitter antenna or a plurality of load impedances, wherein the first plurality of amplified RF signals correspond to a first plurality of constant-envelope signals, and controlling generation of a second plurality of constant-envelope signals on a plurality of transmission paths. The second plurality of constant-envelope signals are generated based on the detected differences of the first plurality of signal characteristics. At least one of first calibrating or second calibrating, a second plurality of signal characteristics of the second plurality of constant-envelope signals. The first calibrating and the second calibrating are based on the controlled generation of the second plurality of constant-envelope signals.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This patent Application is a continuation of U.S. application Ser. No.15/847,367, which was filed on Dec. 19, 2017.

This Application makes reference to:

-   application Ser. No. 15/432,018, which was filed on Feb. 14, 2017,    now U.S. Pat. No. 10,298,275 entitled “Outphasing Transmit and    Receive Wireless Systems Having Dual-Polarized Antennas,”; and-   U.S. Pat. No. 9,935,663, entitled “Low-Loss Isolating Outphasing    Power Combiner in a Radio Frequency Device.”

Each of the above referenced Applications is hereby incorporated hereinby reference in its entirety.

FIELD OF TECHNOLOGY

Certain embodiments of the disclosure relate to outphasing wirelesssystems. More specifically, certain embodiments of the disclosure relateto outphasing calibration in an RF transmitter device.

BACKGROUND

Currently, wireless communication is extensively utilized in variousfields of applications, such as in homes, public places, or officeareas. Consequently, there is a huge demand for high data-rate andbandwidth-efficient wireless transmission standards, such as 802.11Wireless LAN, cellular LTE, and 5G. Accordingly, various concepts, suchas linear amplification using nonlinear components (LINC) (also known asoutphasing), are being used for highly efficient linear poweramplification of wireless signals, for example RF signals.

Typically, in an outphasing transmit wireless system, an RF signal withvarying amplitude (also referred to as “variable-envelope signal”) maybe decomposed into two (or more) components with constant amplitude anddifferent phases (also referred to as “constant-envelope signals”). Suchconstant envelope signals may be amplified by power amplifiers in an RFtransmitter. The two amplified constant-envelope signals may be combinedand transmitted by the RF transmitter, via a multi-antenna array, to anRF receiver.

In certain instances, there may be gain and/or phase mismatches betweenthe two decomposed signals. Consequently, the linearity of the poweramplifiers may be reduced and hence, may increase the error vectormagnitude (EVM) of the RF signal. Further, such mismatch in gain and/orphase may result in IQ imbalance of the RF signal, thus deterioratingthe signal quality. Thus, there is required an outphasing calibrationthat overcomes these deficiencies.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with some aspects of the present disclosureas set forth in the remainder of the present application with referenceto the drawings.

BRIEF SUMMARY OF THE DISCLOSURE

A method and system is provided for an outphasing calibration in an RFtransmitter device, substantially as shown in and/or described inconnection with at least one of the figures, as set forth morecompletely in the claims.

These and other advantages, aspects and novel features of the presentdisclosure, as well as details of an illustrated embodiment thereof,will be more fully understood from the following description anddrawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A illustrates an exemplary wireless system diagram of an exemplaryoutphasing calibration RF transmitter for a first modulated signal, inaccordance with an exemplary embodiment of the disclosure.

FIG. 1B illustrates an exemplary wireless system diagram of an exemplaryoutphasing calibration RF transmitter, as shown in FIG. 1A, for a secondmodulated signal, in accordance with an exemplary embodiment of thedisclosure.

FIG. 2A illustrates a first exemplary embodiment of an outphasingcalibration RF transmitter device.

FIG. 2B illustrates a second exemplary embodiment of an outphasingcalibration RF transmitter device.

FIG. 2C illustrates a third exemplary embodiment of an outphasingcalibration RF transmitter device.

FIG. 2D illustrates a fourth exemplary embodiment of an outphasingcalibration RF transmitter device.

FIG. 3 depicts a flow chart illustrating exemplary operations for anexemplary outphasing calibration RF transmitter of FIGS. 1A and 1B, inaccordance with an exemplary embodiment of the disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

Certain embodiments of the disclosure may be found in a system for anoutphasing calibration RF transmitter device. In the followingdescription, reference is made to the accompanying drawings, which forma part hereof, and in which is shown, by way of illustration, variousembodiments of the present disclosure.

FIG. 1A illustrates an exemplary wireless system diagram of a portion ofan exemplary outphasing calibration RF transmitter for a first modulatedsignal, in accordance with an exemplary embodiment of the disclosure.With reference to FIG. 1A, there is shown an outphasing calibration RFtransmitter 100A that includes a signal decomposition block 102, amemory 103, a first phase shifter (PS) 104A (optional in FIG. 1A), asecond PS 104B (optional in FIG. 1A), a first power amplifier (PA) 106A,a second PA 106B, a first load impedance 108A, a second load impedance108B, a first phase detector (PD) 110A, a second PD 110B, and atransmitter antenna 112. The signal decomposition block 102 may furtherinclude a signal processor 114, a first digital-to-analog converter(DAC) 116A, a second DAC 116B, a first mixer 118A, a second mixer 118B,and a plurality of transmitter signal strength indicator (TSSI) units120A and 120B. There is further shown a first modulated input signal122, a first plurality of constant-envelope signals 124 (such as a firstconstant-envelope signal 124A and a second constant-envelope signal124B), a first plurality of constant-envelope analog signals 126 (suchas a first constant-envelope analog signal 126A and a secondconstant-envelope analog signal 126B), a first plurality of RF signals128 (such as a first RF signal 128A and a second RF signal 128B), afirst plurality of phase-shifted RF signals 130 (optional) (such as afirst phase-shifted RF signal 130A and a second phase-shifted RF signal130B), and a first plurality of amplified RF signals 132 (such as afirst amplified RF signal 132A and a second amplified RF signal 132B).

In accordance with an embodiment, the signal decomposition block 102 maybe coupled to the first PS 104A and the second PS 104B. The first PS104A and the second PS 104B may be further coupled to the first PA 106Aand the second PA 106B. In accordance with another embodiment, thesignal decomposition block 102 may be directly coupled to the first PA106A and the second PA 106B. The first PA 106A and the second PA 106Bmay be differentially coupled to the first load impedance 108A and thesecond load impedance 108B. Further, the first PD 110A and the second PD110B may be differentially coupled to the first load impedance 108A andthe second load impedance 108B, respectively. The transmitter antenna112 may be differentially coupled across the first PA 106A and thesecond PA 106B.

In the signal decomposition block 102, the signal processor 114 iscoupled to the first DAC 116A and the second DAC 116B. Further, thefirst DAC 116A and the second DAC 116B are coupled to the first mixer118A and the second mixer 118B, respectively. It may be noted that thesignal decomposition block 102 may further include additional signalconditioning circuitry, such as phase shifters and time delays in aphased array, without deviation from the scope of the disclosure.

With reference to FIG. 1A, a first modulated input signal 122 may beprovided to the signal decomposition block 102. The first modulatedinput signal 122 is an amplitude and phase modulated signal that may beprovided by, for example a modem (not shown). The first modulated inputsignal 122 is a variable amplitude signal, expressed in equation (1)below:S _(in)(t)=A _(M)*sin(ωt+φ(t))  (1)

-   where, S_(in)(t) represents the first modulated input signal 122,-   A_(M) is the peak value of A(t) that represents the time-varying    amplitude, and-   φ(t) represents outphasing angle.

The signal processor 114 in the signal decomposition block 102 may beconfigured to decompose the first modulated input signal 122 (withvariable amplitude) into the first plurality of constant-envelopesignals 124 on a plurality of transmission paths. The first plurality ofconstant-envelope signals 124 may have a single constant amplitudelevel. The signal processor 114 may be implemented, for example, using afield-programmable gate array (FPGA) or an application-specificintegrated circuit (ASIC) chip. The signal processor 114 may feed thefirst constant-envelope signal 124A and the second constant-envelopesignal 124B to the first DAC 116A and the second DAC 116B, respectively.

The first DAC 116A and the second DAC 116B may be configured to convertthe first plurality of constant-envelope signals 124 into firstplurality of constant-envelope analog signals 126. The first DAC 116Aand the second DAC 116B may feed the first constant-envelope analogsignal 126A and the second constant-envelope analog signal 126B of thefirst plurality of constant-envelope analog signals 126 to the firstmixer 118A and the second mixer 118B, respectively.

The first mixer 118A and the second mixer 118B may be configured toup-convert the first plurality of constant-envelope analog signals 126into the first plurality of RF signals 128. The first RF signal 128A andthe second RF signal 128B of the first plurality of RF signals 128 areexpressed in equations (2) and (3) below:S ₁(t)=A _(M)/2*sin(ωt+φ(t)+ψ(t))  (2)S ₂(t)=A _(M)/2*sin(ωt+φ(t)−ψ(t))  (3)

-   where S₁(t) and S₂(t) represent the first RF signal 128A and the    second RF signal 128B, respectively,-   A_(M) is the peak value of A(t) that represents the time-varying    amplitude, and-   ψ(t) represents arc cos(A(t)).

In accordance with an embodiment, the first mixer 118A and the secondmixer 118B may feed the first RF signal 128A and the second RF signal128B to the first PA 106A and the second PA 106B, respectively. In sucha case, the conversion of the first modulated input signal 122 to thefirst plurality of amplified RF signals 132 is the first instance ofsignal conversion in the outphasing calibration RF transmitter 100A.Thus, the first PS 104A and the second PS 104B may not execute anyphase-shifting of the first plurality of RF signals 128. In accordancewith another embodiment, the first mixer 118A and the second mixer 118Bmay feed the first RF signal 128A and the second RF signal 128B to thefirst PS 104A and the second PS 104B, respectively. The first PS 104Aand the second PS 104B may execute phase-shifting on the first pluralityof RF signals 128 based on various external factors (such as systemconfiguration or manual setting) and not on previous RF signals.Feedback from the first instance(corresponding to the first modulatedinput signal 122) may be provided to a component, such as a modem, basedon which the first PS 104A and the second PS 104B are controlled.Accordingly, the first PS 104A and the second PS 104B may executephase-shifting on next modulated signals, such as a second modulatedinput signal 140, as described in FIG. 1B.

The first PA 106A and the second PA 106B, with similar impedances, maybe configured to amplify the first plurality of RF signals 128, andgenerate the first plurality of amplified RF signals 132. The first PA106A and the second PA 106B may be placed sufficiently apart from eachother and provided respective RF shields for minimization ofinter-modulation or interference between the first PA 106A and thesecond PA 106B.

The first PA 106A and the second PA 106B, operating on the respectivefirst RF signal 128A and the second RF signal 128B, exhibit more powerefficiency and lower back off than a power amplifier that would haveutilized to amplify the first modulated input signal 122 with variableamplitude. Further, the first PA 106A and the second PA 106B operatingon the respective first RF signal 128A and second RF signal 128B,exhibit less non-linearity and introduce less distortion than a poweramplifier that would have utilized to amplify the first modulated inputsignal 122 with variable amplitude. The first PA 106A and the second PA106B may feed the first plurality of amplified RF signals 132 to a powercombiner.

The power combiner may be configured to reconstruct a first output RFsignal based on a combination of the first plurality of amplified RFsignals 132, received from the first PA 106A and the second PA 106B. Thecombination may correspond to a sum (and a difference) of the firstplurality of amplified RF signals 132. In accordance with an embodiment,the combination of the first plurality of amplified RF signals 132 isexpressed in equation (4) below:

$\begin{matrix}\begin{matrix}{{S_{out}(t)} = {{S_{1}^{\prime}(t)} + {S_{2}^{\prime}(t)}}} \\{= {G\;{\cos\left( {\Psi(t)} \right)}{\sin\left( {{\omega\; t} + {\varphi(t)}} \right)}}} \\{= {{{GA}(t)}{\sin\left( {{\omega t} + {\varphi(t)}} \right)}}}\end{matrix} & (4)\end{matrix}$

-   where S_(out)(t) represents the first output RF signal,-   S′₁(t) represents the first amplified RF signal 132A,-   S′₂(t) represents the second amplified RF signal 132B, and-   G represents gain of the amplification stages, i.e. the first PA    106A and the second PA 106B.

The power combiner may be configured to match the impedances of the twoPAs (i.e. the first PA 106A and the second PA 106B) and the transmitterantenna 112. For such impedance matching, the power combiner may utilizevarious components, such as load impedances and transformers. Theprimary coils in the transformers may be utilized to induce current inthe secondary coils for certain currents, generated by two PAs based onthe first plurality of amplified RF signals 132. Further, the loadimpedances may be utilized to dissipate other currents, generated by thetwo PAs based on the first plurality of amplified RF signals 132.Various embodiments of the power combiner have been described in detailin FIGS. 2A to 2D. For example, in accordance with an embodiment asillustrated in FIG. 2A, the primary coils in the transformers may beutilized to induce current in the secondary coils for in-phase currents,generated by two PAs based on the first plurality of amplified RFsignals 132. In such a case, the load impedances may be utilized todissipate out-phase currents, generated by two PAs. Accordingly, thevoltage may be stabilized across the two PAs and the power efficiency ofthe outphasing calibration RF transmitter 100A may be enhanced.

The power combiner may feed the first output RF signal to thetransmitter antenna 112. In accordance with various embodiments, thetransmitter antenna 112 may be a differential antenna (as shown in FIG.2A), a single-ended antenna (as shown in FIG. 2B), or a polarizedantenna (as shown in FIGS. 2C and 2D). The polarized antenna, such as adual-polarized patch antenna, a dual-polarized dipole antenna, or adual-polarized slot antenna, may include a first pair of polarized ports(such as vertical ports) and a second pair of polarized ports (such ashorizontal ports). One or more circuits in the polarized antenna may beconfigured to generate a first signal and a second signal based on thefirst plurality of amplified RF signals 132. The first signal maycorrespond to a sum of the first plurality of amplified RF signals 132.The second signal may correspond to a difference of the first pluralityof amplified RF signals 132. The first pair of polarized ports and thesecond pair of polarized ports of the polarized antenna may beconfigured to transmit the first signal and the second signal to anoutphasing RF receiver, via an RF communication network. Such anoutphasing RF receiver may receive and process the first and the secondsignal, received from the outphasing calibration RF transmitter 100A.

In accordance with an embodiment, the first PD 110A and the second PD110B, differentially coupled to the first load impedance 108A and thesecond load impedance 108B, may be configured to detect differences of afirst signal characteristic, such as a phase difference, of the firstplurality of amplified RF signals 132 across the first load impedance108A and the second load impedance 108B. The first PD 110A and thesecond PD 110B may be configured to transmit the detected phasedifference to a first controller (not shown), such as a phasecontroller, to control a phase difference of next modulated inputsignal, such as the second modulated input signal 140 (as shown in FIG.1B).

In accordance with an embodiment, the first TSSI unit 120A may bedifferentially coupled to the first PA 106A and the second TSSI unit120B may be differentially coupled to the second PA 106B. The TSSI units120A and 120B may be configured to detect differences of a second signalcharacteristic, such as a voltage differences, of the first plurality ofamplified RF signals 132 across the first PA 106A and the second PA106B. The TSSI units 120A and 120B may be configured to transmit thedetected voltage difference to a second controller (not shown), such asmodem, to control a gain difference of next modulated input signal, suchas the second modulated input signal 140 (as shown in FIG. 1B).

FIG. 1B illustrates an exemplary wireless system diagram of a portion ofan exemplary outphasing calibration RF transmitter, as shown in FIG. 1A,for a second modulated signal, in accordance with an exemplaryembodiment of the disclosure. With reference to FIG. 1B, there is shownthe outphasing calibration RF transmitter 100B, as shown in FIG. 1A.Similar to the outphasing calibration RF transmitter 100A, theoutphasing calibration RF transmitter 100B includes various components,such as the signal decomposition block 102, a memory 103, the first PS104A, the second PS 104B, the first PA 106A, the second PA 106B, thefirst load impedance 108A, the second load impedance 108B, the first PD110A, the second PD 110B, and the transmitter antenna 112. The signaldecomposition block 102 may further include the signal processor 114,the first DAC 116A, the second DAC 116B, the first mixer 118A, and thesecond mixer 118B, and the plurality of TSSI units 120A and 120B.

There is further shown the second modulated input signal 140, a secondplurality of constant-envelope signals 142 (such as a firstconstant-envelope signal 142A and a second constant-envelope signal142B), a second plurality of constant-envelope analog signals 144 (suchas a first constant-envelope analog signal 144A and a secondconstant-envelope analog signal 144B), a second plurality of RF signals146 (such as a first RF signal 146A and a second RF signal 146B), asecond plurality of phase-shifted RF signals 148 (such as a firstphase-shifted RF signal 148A and a second phase-shifted RF signal 148B),and a second plurality of amplified RF signals 150 (such as a firstamplified RF signal 150A and a second amplified RF signal 150B).

With reference to FIG. 1B, the second modulated input signal 140 may beprovided to the signal decomposition block 102. The second modulatedinput signal 140 is an amplitude and phase modulated signal that may beprovided by, for example a modem (not shown). The second modulated inputsignal 140 is a variable amplitude signal, expressed in equation (1), asdescribed in FIG. 1A.

The signal processor 114 in the signal decomposition block 102 mayfurther receive a feedback signal characteristic, such as a voltagedifference, from the second controller. The voltage difference,corresponding to the first modulated input signal 122, is determined bythe TSSI units 120A and 120B and provided to the second controller forcalibration of a second plurality of signal characteristics, such asgain mismatch, that corresponds to the second plurality ofconstant-envelope signals 142. The second plurality of constant-envelopesignals 142, thus generated by the signal processor 114 postcalibration, exhibits reduced gain mismatch as compared to the firstplurality of constant-envelope signals 124.

The signal processor 114 may feed the second plurality ofconstant-envelope signals 142 to the first DAC 116A and the second DAC116B, respectively. The first DAC 116A and the second DAC 116B may beconfigured to convert the second plurality of constant-envelope signals142 into second plurality of constant-envelope analog signals 144. Thefirst DAC 116A and the second DAC 116B may feed the firstconstant-envelope analog signal 144A and the second constant-envelopeanalog signal 144B of the second plurality of constant-envelope analogsignals 144 to the first mixer 118A and the second mixer 118B,respectively.

The first mixer 118A and the second mixer 118B may be configured toup-convert the second plurality of constant-envelope analog signals 144into the second plurality of RF signals 146. The first RF signal 146Aand the second RF signal 146B of the second plurality of RF signals 146are expressed in equations (2) and (3), as described in FIG. 1A.

The first mixer 118A and the second mixer 118B may feed the first RFsignal 146A and the second RF signal 146B to the first PS 104A and thesecond PS 104B, respectively. The first PS 104A and the second PS 104Bmay further receive a feedback signal characteristic, such as a phasedifference, from the first controller. The phase difference,corresponding to the first modulated input signal 122, may be determinedby the first PD 110A and the second PD 110B, and provided to the firstcontroller for calibration of the second plurality of signalcharacteristics, such as phase mismatch, that corresponds to the secondplurality of RF signals 146. The second plurality of phase-shifted RFsignals 148, thus generated by the first PS 104A and the second PS 104Bpost calibration, exhibits reduced phase mismatch as compared to thefirst plurality of RF signals 128.

The first PS 104A and the second PS 104B may be configured to feed thesecond plurality of phase-shifted RF signals 148 to the first PA 106Aand the second PA 106B, respectively. The first PA 106A and the secondPA 106B, with similar impedances, may be configured to amplify thesecond plurality of phase-shifted RF signals 148, and generate thesecond plurality of amplified RF signals 150. The second plurality ofamplified RF signals 150, thus generated by the first PA 106A and thesecond PA 106B, exhibits reduced differences of a second plurality ofsignal characteristics, such as gain and/or phase mismatch, of thesecond plurality of amplified RF signals 150, as compared to the firstplurality of signal characteristics of the first plurality of amplifiedRF signals 132.

The power combiner may be configured to reconstruct a second output RFsignal based on a combination of the second plurality of amplified RFsignals 150, received from the first PA 106A and the second PA 106B. Thecombination may correspond to a sum (and a difference) of the secondplurality of amplified RF signals 150. In accordance with an embodiment,the combination of the second plurality of amplified RF signals 150 isexpressed in equation (4), as described in FIG. 1A.

Thus, the outphasing calibration RF transmitter 100B may be configuredto reduce the gain, phase, and/or outphasing mismatches between twodecomposed signals based on calibration of second plurality of signalcharacteristics of the second plurality of constant-envelope signals.Consequently, the linearity of the first PA 106A and the second PA 106Bis reduced and hence, increases the error vector magnitude (EVM) of theRF signal. Further, such reduction in the mismatch in gain and/or phasemay correct the IQ imbalance of the RF signal, thus improving the signalquality of an output RF signal, such as the second output RF signal.

FIG. 2A illustrates a first exemplary embodiment of an exemplaryoutphasing calibration RF transmitter. With reference to FIG. 2A, thereis shown a portion of the outphasing calibration RF transmitter 100Athat includes the first PA 106A, the second PA 106B, and a differentialantenna 112A. There is further shown a transformer in a power combinerof the outphasing calibration RF transmitter 100A. The transformer mayinclude a first primary coil 202A, a second primary coil 202B, and asecondary coil 202C. The power combiner may further include the firstload impedance 108A, the second load impedance 108B, the first PD 110A,the second PD 110B, and a TSSI 204.

The first primary coil 202A is coupled to the first PA 106A and thesecond primary coil 202B is coupled to the second PA 106B. The secondarycoil 202C is coupled with the first primary coil 202A and the secondprimary coil 202B on one side, and with the differential antenna 112A onthe other side. The first load impedance 108A is adjustable and coupledbetween first terminals of the first PA 106A and the second PA 106B.Similarly, the second load impedance 108B is adjustable and coupledbetween second terminals of the first PA 106A and the second PA 106B. Itmay be noted that in a first implementation of the first exemplaryembodiment, as shown in FIG. 2A, the first terminals correspond to thepositive terminals of the first PA 106A and the second PA 106B, and thesecond terminals correspond to the negative terminals of the first PA106A and the second PA 106B. In a second implementation of the firstexemplary embodiment, the first terminals correspond to the positiveterminal of the first PA 106A and the negative terminal of the second PA106B, and the second terminals correspond to the negative terminal ofthe first PA 106A and the positive terminal of the second PA 106B.

With reference to FIG. 2A, in accordance with the first implementationof the first exemplary embodiment, the first PA 106A receives the firstRF signal 128A and generates the first amplified RF signal 132A.Similarly, the second PA 106B receives the second RF signal 128B andgenerates the second amplified RF signal 132B. Due to the firstamplified RF signal 132A, a first current I₁ is generated across theoutput terminals of the first PA 106A. Similarly, due to the secondamplified RF signal 132B, a second current I₂ is generated across theoutput terminals of the second PA 106B.

In accordance with the first implementation of the first exemplaryembodiment, the first current I₁ is in-phase with the second current I₂.In other words, a first phase of the first amplified RF signal 132A inthe first primary coil 202A is in the same direction with respect to asecond phase of the second amplified RF signal 132B in the secondprimary coil 202B. In such a case, a current I₃ may be induced in thesecondary coil 202C of the transformer. The secondary coil 202C maysupply the current I₃ to the differential antenna 112A. Hence, the TSSI204 may detect a difference of a first plurality of signalcharacteristics, such as voltage difference, of the first plurality ofamplified RF signals 132 across the differential antenna 112A. At thesame time, there is zero potential drop across the first terminals ofthe first PA 106A and the second PA 106B and the second terminals of thefirst PA 106A and the second PA 106B. Thus, no current is dissipated inthe first load impedance 108A and the second load impedance 108B. Hence,the first PD 110A and the second PD 110B may not detect differences of afirst plurality of signal characteristics, such as phase differences, ofthe first plurality of amplified RF signals 132 across the plurality ofload impedances 108.

Thus, in accordance with the first implementation of the first exemplaryembodiment, the TSSI 204 may be configured to communicate the detecteddifference of the first plurality of signal characteristics, i.e. thevoltage difference, to the second controller, such as a modem. Thesecond controller may be configured to control the signal processor 114for the generation of the second plurality of constant-envelope signals142 on the plurality of transmission paths. Thus, a first calibration ofthe second plurality of signal characteristics of the second pluralityof constant-envelope signals 142 is executed to reduce the differencesof the second plurality of signal characteristics of the secondplurality of constant-envelope signals 142.

In accordance with the second implementation of the first exemplaryembodiment, as described above, the first terminals correspond to thepositive terminal of the first PA 106A and the negative terminal of thesecond PA 106B. Further, the second terminals correspond to the negativeterminal of the first PA 106A and the positive terminal of the second PA106B. In such an implementation, the first current I₁ is out-phased withthe second current I₂. In other words, a first phase of the firstamplified RF signal 132A in the first primary coil 202A is in theopposite direction with respect to a second phase of the secondamplified RF signal 132B in the second primary coil 202B. In such acase, no current may be induced in the secondary coil 202C of thetransformer. Thus, the secondary coil 202C may not supply any current tothe differential antenna 112A. Hence, the TSSI 204 may not detect adifference of a first plurality of signal characteristics, such asvoltage difference, of the first plurality of amplified RF signals 132across the differential antenna 112A. At the same time (concurrently),there is a potential drop across the first terminals of the first PA106A and the second PA 106B and the second terminals of the first PA106A and the second PA 106B. Thus, the currents I₁ and I₂ are dissipatedin the first load impedance 108A and the second load impedance 108B,respectively. Hence, the first PD 110A and the second PD 110B may detectdifferences of a first plurality of signal characteristics, such asphase differences, of the first plurality of amplified RF signals 132across the plurality of load impedances 108.

Thus, in accordance with the second implementation of the firstexemplary embodiment, the first PD 110A and the second PD 110B may beconfigured to communicate the detected difference of the first pluralityof signal characteristics, i.e. the phase difference, to the firstcontroller, such as a phase controller. The first controller may beconfigured to control the first PS 104A and the second PS 104B. Thefirst PS 104A and the second PS 104B further control the secondplurality of signal characteristics, such as a phase difference, of thesecond plurality of constant-envelope signals 142 on the plurality oftransmission paths. Thus, a second calibration of the second pluralityof signal characteristics of the second plurality of constant-envelopesignals 142 is executed to reduce the differences of the secondplurality of signal characteristics of the second plurality ofconstant-envelope signals 142.

FIG. 2B illustrates a second exemplary embodiment of an exemplaryoutphasing calibration RF transmitter. With reference to FIG. 2B, thereis shown a portion of the outphasing calibration RF transmitter 100Athat includes the first PA 106A, the second PA 106B, and a single-endedantenna 112B with one end connected to the ground. There is furthershown the first primary coil 202A, the second primary coil 202B, and thesecondary coil 202C in the transformer of a power combiner. The powercombiner may further include the first load impedance 108A, the secondload impedance 108B, the first PD 110A, and the second PD 110B. There isfurther shown the TSSI 204 coupled across the single-ended antenna 112B.

The first primary coil 202A is coupled to positive terminals of thefirst PA 106A and the second PA 106B. The second primary coil 202B iscoupled to negative terminals of the first PA 106A and the second PA106B. One end of the secondary coil 202C is coupled to the first primarycoil 202A, the second primary coil 202B, and the single-ended antenna112B. Other end of the secondary coil 202C is grounded. The first loadimpedance 108A is coupled between first terminals of the first PA 106Aand the second PA 106B. Similarly, the second load impedance 108B iscoupled between second terminals of the first PA 106A and the second PA106B. It may be noted that in the first implementation of the secondexemplary embodiment, as shown in FIG. 2B, the first terminalscorrespond to the positive terminal of the first PA 106A and thepositive terminal of the second PA 106B, and the second terminalscorrespond to the negative terminal of the first PA 106A and thenegative terminal of the second PA 106B. In a second implementation ofthe second exemplary embodiment, the first terminals correspond to thepositive terminal of the first PA 106A and the negative terminal of thesecond PA 106B, and the second terminals correspond to the negativeterminal of the first PA 106A and the positive terminal of the second PA106B.

With reference to FIG. 2B, in accordance with the first implementationof the second exemplary embodiment, the first PA 106A receives the firstRF signal 128A and generates the first amplified RF signal 132A.Similarly, the second PA 106B receives the second RF signal 128B andgenerates the second amplified RF signal 132B. Due to the firstamplified RF signal 132A, a first current I₁ is generated across theoutput terminals of the first PA 106A. Similarly, due to the secondamplified RF signal 132B, a second current I₂ is generated across theoutput terminals of the second PA 106B.

In accordance with the first implementation of the second exemplaryembodiment, there is no potential drop across the first terminals of thefirst PA 106A and the second PA 106B and the second terminals of thefirst PA 106A and the second PA 106B. Thus, a current is not dissipatedin the first load impedance 108A and the second load impedance 108B andconsequently, the first current I₁ will flow through the first primarycoil 202A and the second current I₂ (that is in-phase with the firstcurrent I₁) will flow through the second primary coil 202B. Hence, thefirst PD 110A and the second PD 110B may not detect differences of afirst plurality of signal characteristics, such as phase differences, ofthe first plurality of amplified RF signals 132 across the plurality ofload impedances 108. However, the third current I₃ is induced in thesecondary coil 202C, and is supplied to the single-ended antenna 112B.Hence, the TSSI 204 may detect a difference of a first plurality ofsignal characteristics, such as voltage difference, of the firstplurality of amplified RF signals 132 across the single-ended antenna112B.

Thus, in accordance with the first implementation of the secondexemplary embodiment, the TSSI 204 may be configured to communicate thedetected difference of the first plurality of signal characteristics,i.e. the voltage difference, to the second controller, such as a modem.The second controller may be configured to control the signal processor114 for the generation of the second plurality of constant-envelopesignals 142 on the plurality of transmission paths. Thus, a firstcalibration of the second plurality of signal characteristics of thesecond plurality of constant-envelope signals 142 is executed to reducethe differences of the second plurality of signal characteristics of thesecond plurality of constant-envelope signals 142.

In accordance with the second implementation of the second exemplaryembodiment, as described above, there is a potential drop across thefirst terminals of the first PA 106A and the second PA 106B and thesecond terminals of the first PA 106A and the second PA 106B. Thus,current is dissipated in the first load impedance 108A and the secondload impedance 108B. Hence, the first PD 110A and the second PD 110B maydetect differences of a first plurality of signal characteristics, suchas phase differences, of the first plurality of amplified RF signals 132across the plurality of load impedances 108. Consequently, no currentwill flow through the first primary coil 202A and the second primarycoil 202B. In such implementation, no current is induced in thesecondary coil 202C and thus, no current is supplied to the single-endedantenna 112B. Hence, the TSSI 204 may not detect a difference of a firstplurality of signal characteristics, such as voltage difference, of thefirst plurality of amplified RF signals 132 across the single-endedantenna 112B.

Thus, in accordance with the second implementation of the secondexemplary embodiment, the first PD 110A and the second PD 110B may beconfigured to communicate the detected difference of the first pluralityof signal characteristics, i.e. the phase difference, to the firstcontroller, such as a phase controller. The first controller may beconfigured to control the first PS 104A and the second PS 104B. Thefirst PS 104A and the second PS 104B further control the secondplurality of signal characteristics of the second plurality ofconstant-envelope signals 142 on the plurality of transmission paths.Thus, a second calibration of the second plurality of signalcharacteristics of the second plurality of constant-envelope signals 142is executed to reduce the differences of the second plurality of signalcharacteristics of the second plurality of constant-envelope signals142.

FIG. 2C illustrates a third exemplary embodiment of an exemplaryoutphasing calibration RF transmitter. With reference to FIG. 2C, thereis shown a portion of the outphasing calibration RF transmitter 100Athat includes the first PA 106A, the second PA 106B, and a polarizedantenna 112C. The power combiner may further include a first transformer206 and a second transformer 208. The first transformer 206 may includea primary coil 206A and a secondary coil 206B. Similarly, the secondtransformer 208 may include a primary coil 208A and a secondary coil208B. The polarized antenna 112C includes a first pair of polarizedports and a second pair of polarized ports. The first TSSI unit 120A iscoupled across the first pair of polarized ports and the second TSSIunit 120B is coupled across the second pair of polarized ports. Thefirst pair of polarized ports is coupled with the secondary coil 206B ofthe first transformer 206. The second pair of polarized ports is coupledto the secondary coil 208B of the second transformer 208. There isfurther shown a first load impedance 108A and a second load impedance108B. The first load impedance 108A is coupled to the first terminals ofthe secondary coil 206B and the secondary coil 208B. The second loadimpedance 108B is coupled to the second terminals of the secondary coil206B and the secondary coil 208B. In accordance with a firstimplementation of the third exemplary embodiment, the first terminalscorrespond to the positive terminals of the secondary coil 206B and thesecondary coil 208B. Further, the second terminals correspond to thenegative terminals of the secondary coil 206B and the secondary coil208B. In accordance with a second implementation of the third exemplaryembodiment, the first terminals correspond to the positive terminal ofthe secondary coil 206B and the negative terminal of the secondary coil208B. Further, the second terminals correspond to the negative terminalof the secondary coil 206B and the positive terminal of the secondarycoil 208B.

With reference to FIG. 2C, in accordance with the first implementationof the third exemplary embodiment, the first PA 106A receives the firstRF signal 128A and generates the first amplified RF signal 132A.Similarly, the second PA 106B receives the second RF signal 128B andgenerates the second amplified RF signal 132B. Due to the firstamplified RF signal 132A, a first current I_(P1) is generated across theoutput terminals of the first PA 106A. Similarly, due to the secondamplified RF signal 132B, a second current I_(P2) is generated acrossthe output terminals of the second PA 106B.

In accordance with the first implementation of the third exemplaryembodiment, the first current I_(P1) in the primary coil 206A isin-phase with the second current I_(P2) in the primary coil 208A. Inother words, a first phase of the first amplified RF signal 132A in theprimary coil 206A is in the same direction with respect to a secondphase of the second amplified RF signal 132B in the primary coil 208A.In such a case, a current I_(S1) may be induced in the secondary coil206B of the first transformer 206 and a current I_(S2) may be induced inthe secondary coil 208B of the second transformer 208. Consequently,there are no potential drops across the first load impedance 108A andthe second load impedance 108B. Thus, the currents I_(S1) and I_(S2) arenot dissipated across the first load impedance 108A and the second loadimpedance 108B and the currents I_(S1) and I_(S2) are supplied to thepolarized antenna 112C. Hence, the first TSSI unit 120A and the secondTSSI unit 120B may detect difference of a first plurality of signalcharacteristics, such as voltage differences, of the first plurality ofamplified RF signals 132 across the first pair of polarized ports andthe second pair of polarized ports of the polarized antenna 112C.

Thus, in accordance with the first implementation of the third exemplaryembodiment, the first TSSI unit 120A and the second TSSI unit 120B maybe configured to communicate the detected differences of the firstplurality of signal characteristics, i.e. the voltage differences, tothe second controller, such as a modem. The second controller may beconfigured to control the signal processor 114 for the generation of thesecond plurality of constant-envelope signals 142 on the plurality oftransmission paths. Thus, a first calibration of the second plurality ofsignal characteristics of the second plurality of constant-envelopesignals 142 is executed to reduce the differences of the secondplurality of signal characteristics of the second plurality ofconstant-envelope signals 142.

In accordance with the second implementation of the third exemplaryembodiment, as described above, the first current I_(P1) is outphasedwith the second current I_(P2). In other words, a first phase of thefirst amplified RF signal 132A in the primary coil 206A is in theopposite direction with respect to a second phase of the secondamplified RF signal 132B in the secondary coil 208B. In such a case, thecurrent I_(S1) may be induced in the secondary coil 206B of the firsttransformer 206 and a current I_(S2) may be induced in the secondarycoil 208B of the second transformer 208. Consequently, there arepotential drops across the first load impedance 108A and the second loadimpedance 108B. Thus, the currents I_(S1) and I_(S2) are dissipatedacross the first load impedance 108A and the second load impedance 108Band the currents I_(S1) and I_(S2) are not supplied to the polarizedantenna 112C. Hence, the first PD 110A and the second PD 110B may detectdifferences of a first plurality of signal characteristics, such asphase differences, of the first plurality of amplified RF signals 132across the plurality of load impedances 108.

Thus, in accordance with the second implementation of the thirdexemplary embodiment, the first PD 110A and the second PD 110B may beconfigured to communicate the detected difference of the first pluralityof signal characteristics, i.e. the phase difference, to the firstcontroller, such as a phase controller. The first controller may beconfigured to control the first PS 104A and the second PS 104B. Thefirst PS 104A and the second PS 104B further control the secondplurality of signal characteristics of the second plurality ofconstant-envelope signals 142 on the plurality of transmission paths.Thus, a second calibration of the second plurality of signalcharacteristics of the second plurality of constant-envelope signals 142is executed to reduce the differences of the second plurality of signalcharacteristics of the second plurality of constant-envelope signals142.

FIG. 2D illustrates a fourth exemplary embodiment of an exemplaryoutphasing calibration RF transmitter. With reference to FIG. 2D, thereis shown a portion of the outphasing calibration RF transmitter 100Athat includes the first PA 106A, the second PA 106B, and the polarizedantenna 112C. The power combiner may further include the first loadimpedance 108A and the second load impedance 108B. The polarized antenna112C includes a first pair of polarized ports and a second pair ofpolarized ports. A first TSSI unit 120A is coupled across the first pairof polarized ports and a second TSSI unit 120B is coupled across thesecond pair of polarized ports. The first pair of polarized ports iscoupled with the first PA 106A. The second pair of polarized ports iscoupled to the second PA 106B.

The first load impedance 108A is coupled to the first terminals of thefirst PA 106A and the second PA 106B. The second load impedance 108B iscoupled to the second terminals of the first PA 106A and the second PA106B. In accordance with a first implementation of the fourth exemplaryembodiment, the first terminals correspond to the positive terminals ofthe first PA 106A and the second PA 106B. Further, the second terminalscorrespond to the negative terminals of the first PA 106A and the secondPA 106B. In accordance with a second implementation of the fourthexemplary embodiment, the first terminals correspond to the positiveterminal of the first PA 106A and the negative terminal of the second PA106B. Further, the second terminals correspond to the negative terminalof the first PA 106A and the positive terminal of the second PA 106B.

With reference to FIG. 2D, in accordance with the first implementationof the fourth exemplary embodiment, the first PA 106A receives the firstRF signal 128A and generates the first amplified RF signal 132A.Similarly, the second PA 106B receives the second RF signal 128B andgenerates the second amplified RF signal 132B. Due to the firstamplified RF signal 132A, a first current I₁ is generated across theoutput terminals of the first PA 106A. Similarly, due to the secondamplified RF signal 132B, a second current I₂ is generated across theoutput terminals of the second PA 106B.

In accordance with the first implementation of the fourth exemplaryembodiment, when currents I₁ and I₂ are in-phase, there are no potentialdrops across the first load impedance 108A and the second load impedance108B. Thus, the currents I₁ and I₂ are not dissipated across the firstload impedance 108A and the second load impedance 108B and the currentsI₁ and I₂ are supplied to the polarized antenna 112C. Hence, the firstTSSI unit 120A and the second TSSI unit 120B may detect difference of afirst plurality of signal characteristics, such as voltage difference,of the first plurality of amplified RF signals 132 across the first pairof polarized ports and the second pair of polarized ports of thepolarized antenna 112C.

Thus, in accordance with the first implementation of the fourthexemplary embodiment, the first TSSI unit 120A and the second TSSI unit120B may be configured to communicate the detected difference of thefirst plurality of signal characteristics, i.e. the voltage difference,to the second controller, such as a modem. The second controller may beconfigured to control the signal processor 114 for the generation of thesecond plurality of constant-envelope signals 142 on the plurality oftransmission paths. Thus, a first calibration of the second plurality ofsignal characteristics of the second plurality of constant-envelopesignals 142 is executed to reduce the differences of the secondplurality of signal characteristics of the second plurality ofconstant-envelope signals 142.

In accordance with the second implementation of the fourth exemplaryembodiment, as described above, when currents I₁ and I₂ are outphased,there are potential drops across the first load impedance 108A and thesecond load impedance 108B. Thus, the currents I₁ and I₂ are dissipatedacross the first load impedance 108A and the second load impedance 108Band the currents I₁ and I₂ are not supplied to the polarized antenna112C. Hence, the first PD 110A and the second PD 110B may detectdifferences of a first plurality of signal characteristics, such asphase differences, of the first plurality of amplified RF signals 132across the plurality of load impedances 108.

Thus, in accordance with the second implementation of the fourthexemplary embodiment, the first PD 110A and the second PD 110B may beconfigured to communicate the detected difference of the first pluralityof signal characteristics, i.e. the phase difference, to the firstcontroller, such as a phase controller. The first controller may beconfigured to control the first PS 104A and the second PS 104B. Thefirst PS 104A and the second PS 104B further control the secondplurality of signal characteristics of the second plurality ofconstant-envelope signals 142 on the plurality of transmission paths.Thus, a second calibration of the second plurality of signalcharacteristics of the second plurality of constant-envelope signals 142is executed to reduce the differences of the second plurality of signalcharacteristics of the second plurality of constant-envelope signals142.

FIG. 3 depicts a flow chart illustrating exemplary operations for anexemplary outphasing calibration RF transmitter of FIGS. 1A and 1B, inaccordance with an exemplary embodiment of the disclosure. Referring toFIG. 3, there is shown a flow chart 300 comprising exemplary operations302 through 318.

At 302, a first plurality of constant-envelope signals may be generated.In accordance with an embodiment, the signal processor 114 in the signaldecomposition block 102 may be configured to generate the firstplurality of constant-envelope signals 124 based on outphasing (ordecomposition) of the first modulated input signal 122. The firstmodulated input signal 122 may be a modulated signal with variableamplitude received from a modem, for example. The first plurality ofconstant-envelope signals 124, thus generated, may have a singleconstant amplitude level.

At 304, the first plurality of constant-envelope signal may be convertedinto a first plurality of constant-envelope analog signals. Inaccordance with an embodiment, the first DAC 116A and the second DAC116B may be configured to convert the first plurality ofconstant-envelope signals 124 into first plurality of constant-envelopeanalog signals 126. The first DAC 116A and the second DAC 116B may feedthe first constant-envelope analog signal 126A and the secondconstant-envelope analog signal 126B of the first plurality ofconstant-envelope analog signals 126 to the first mixer 118A and thesecond mixer 118B, respectively.

At 306, the first plurality of constant-envelope analog signals may beup-converted into a first plurality of RF signals. In accordance with anembodiment, the first mixer 118A and the second mixer 118B may beconfigured to up-convert the first plurality of constant-envelope analogsignals 126 into the first plurality of RF signals 128 based on localoscillations generated by a local oscillator. The first RF signal 128Aand the second RF signal 128B of the first plurality of RF signals 128are expressed in equations (2) and (3), as described in FIG. 1A.

At 308, the first plurality of RF signals may be amplified. Inaccordance with an embodiment, the first PA 106A and the second PA 106B,with similar impedances, may be configured to amplify the firstplurality of RF signals 128, and generate the first plurality ofamplified RF signals 132. The first PA 106A and the second PA 106B maybe placed sufficiently apart from each other and provided respective RFshields for minimization of inter-modulation or interference between thefirst PA 106A and the second PA 106B.

In accordance with an embodiment, prior to the amplification, phaseshifting may be performed on the first plurality of RF signals 128 tocontrol phase difference between the first plurality of RF signals 128.Such phase shifting on the first plurality of RF signals 128 isperformed based on external factors, such as system configuration ormanual setting. The phase shifting of the first plurality of RF signals128 is not based on previous signals. Thus, this step may be an optionalstep for the first plurality of RF signals 128.

At 310, the first plurality of amplified RF signals 132 may be combined.In accordance with an embodiment, the power combiner may be configuredto reconstruct a first output RF signal based on a combination of thefirst plurality of amplified RF signals 132, received from the first PA106A and the second PA 106B. The combination may correspond to a sum(and a difference) of the first plurality of amplified RF signals 132.In accordance with an embodiment, the combination of the first pluralityof amplified RF signals 132 is expressed in equation (4), as describedin FIG. 1B.

At 312, differences of a first plurality of signal characteristics ofthe first plurality of amplified RF signals may be detected. Thedifferences may be detected by one or more electronic components basedon in-phased or out-phased currents generated across the first PA 106Aand the second PA 106B. In accordance with an embodiment, when thecurrents are dissipated in the first load impedance 108A and the secondload impedance 108B (for example, in accordance with the secondimplementation of the first exemplary embodiment (FIG. 2A)), the firstPD 110A and the second PD 110B may be configured to detect differencesof a first signal characteristic, such as a phase difference, across thefirst load impedance 108A and the second load impedance 108B.

In accordance with another embodiment, when the currents are dissipatedin the differential antenna 112A (for example, in accordance with thefirst implementation of the first exemplary embodiment (FIG. 2A)), theTSSI 204 may be configured to detect differences of a first signalcharacteristic, such as a voltage difference, across the differentialantenna 112A.

At 314, detected differences of the first plurality of signalcharacteristics of the first plurality of amplified signals may betransmitted. In accordance with an embodiment, the first PD 110A and thesecond PD 110B may be configured to transmit the detected phasedifference to a first controller (not shown), such as a phasecontroller, to control a phase difference of next modulated inputsignal, such as the second modulated input signal 140. In accordancewith another embodiment, the TSSI 204 may be configured to transmit thedetected phase difference to a second controller (not shown), such as amodem, to control a gain difference of next modulated input signal, suchas the second modulated input signal 140.

At 316, based on the detected differences of the first plurality ofsignal characteristics, at least a generation of a second plurality ofconstant-envelope signals and at least one signal characteristic of eachof a second plurality of constant-envelope RF signals on the pluralityof transmission paths may be controlled. In accordance with anembodiment, the first controller may be configured to control the firstPS 104A and the second PS 104B. The first PS 104A and the second PS 104Bfurther control the second plurality of signal characteristics of thesecond plurality of constant-envelope signals 142 on the plurality oftransmission paths. In accordance with another embodiment, the secondcontroller may be configured to control the signal processor 114 for thegeneration of the second plurality of constant-envelope signals 142 onthe plurality of transmission paths.

At 318, at least one of the first calibration and a second calibrationof the second plurality of signal characteristics of the secondplurality of constant-envelope signals may be executed. In accordancewith an embodiment, at least one of the first calibration and the secondcalibration of the second plurality of signal characteristics of thesecond plurality of constant-envelope signals 142 is executed to reducethe differences of the second plurality of signal characteristics of thesecond plurality of constant-envelope signals 142.

Thus, the outphasing calibration RF transmitter 100B may be configuredto reduce the gain, phase, and/or outphasing mismatches between twodecomposed signals based on calibration of second plurality of signalcharacteristics of the second plurality of constant-envelope signals142. Consequently, the linearity of the first PA 106A and the second PA106B is reduced and hence, increases the error vector magnitude (EVM) ofthe second output RF signal. Further, such reduction in the mismatch ingain and/or phase may correct the IQ imbalance of the second output RFsignal, thus improving the signal quality of the second output RFsignal.

While various embodiments described in the present disclosure have beendescribed above, it should be understood that they have been presentedby way of example, and not limitation. It is to be understood thatvarious changes in form and detail can be made therein without departingfrom the scope of the present disclosure. In addition to using hardware(e.g., within or coupled to a central processing unit (“CPU” orprocessor), microprocessor, micro controller, digital signal processor,processor core, system on chip (“SOC”) or any other device),implementations may also be embodied in software (e.g. computer readablecode, program code, and/or instructions disposed in any form, such assource, object or machine language) disposed for example in anon-transitory computer-readable medium configured to store thesoftware. Such software can enable, for example, the function,fabrication, modeling, simulation, description and/or testing of theapparatus and methods describe herein. For example, this can beaccomplished through the use of general program languages (e.g., C,C++), hardware description languages (HDL) including Verilog HDL, VHDL,and so on, or other available programs. Such software can be disposed inany known non-transitory computer-readable medium, such assemiconductor, magnetic disc, or optical disc (e.g., CD-ROM, DVD-ROM,etc.). The software can also be disposed as computer data embodied in anon-transitory computer-readable transmission medium (e.g., solid statememory any other non-transitory medium including digital, optical,analogue-based medium, such as removable storage media). Embodiments ofthe present disclosure may include methods of providing the apparatusdescribed herein by providing software describing the apparatus andsubsequently transmitting the software as a computer data signal over acommunication network including the internet and intranets.

It is to be further understood that the system described herein may beincluded in a semiconductor intellectual property core, such as amicroprocessor core (e.g., embodied in HDL) and transformed to hardwarein the production of integrated circuits. Additionally, the systemdescribed herein may be embodied as a combination of hardware andsoftware. Thus, the present disclosure should not be limited by any ofthe above-described exemplary embodiments, but should be defined only inaccordance with the following claims and their equivalents.

What is claimed is:
 1. An outphasing calibration method, comprising: detecting, by a circuitry in an outphasing radio frequency (RF) transmitter, differences of a first plurality of signal characteristics of a first plurality of amplified RF signals across at least a transmitter antenna or a plurality of load impedances, wherein the first plurality of amplified RF signals correspond to a first plurality of constant-envelope signals; controlling, by the circuitry, generation of a second plurality of constant-envelope signals, wherein the second plurality of constant-envelope signals are generated on a plurality of transmission paths, wherein the second plurality of constant-envelope signals are generated based on the detected differences of the first plurality of signal characteristics; and at least one of first calibrating, by the circuitry, or second calibrating, by the circuitry, a second plurality of signal characteristics of the second plurality of constant-envelope signals, wherein the first calibrating and the second calibrating are based on the controlled generation of the second plurality of constant-envelope signals.
 2. The outphasing calibration method according to claim 1, further comprising: generating, by the circuitry, the first plurality of constant-envelope signals based on a first out-phasing of a first modulated input signal, and generating, by the circuitry, the second plurality of constant-envelope signals based on a second out-phasing of a second modulated input signal, wherein the first plurality of constant-envelope signals and the second plurality of constant-envelope signals comprises digital signals with constant amplitudes.
 3. The outphasing calibration method according to claim 2, wherein the first modulated input signal and the second modulated input signal have variable amplitudes, wherein first phases of at least two signals of the first plurality of constant-envelope signals are in opposite directions and second phases of at least two signals of the second plurality of constant-envelope signals are in opposite directions, and wherein the transmitter antenna corresponds to at least one of a polarized antenna, a differential antenna, or a single-ended antenna.
 4. The outphasing calibration method according to claim 1, further comprising: converting, by the circuitry, the first plurality of constant-envelope signals into a first plurality of constant-envelope analog signals, and converting, by the circuitry, the second plurality of constant-envelope signals into a second plurality of constant-envelope analog signals.
 5. The outphasing calibration method according to claim 4, further comprising: up-converting, by the circuitry, the first plurality of constant-envelope analog signals into a first plurality of RF signals, and up-converting, by the circuitry, the second plurality of constant-envelope analog signals into a second plurality of RF signals, wherein the first plurality of RF signals and the second plurality of RF signals are up-converted based on local oscillations.
 6. The outphasing calibration method according to claim 5, further comprising phase-shifting, by the circuitry, each of the second plurality of RF signals with a defined value to generate a second plurality of phase-shifted RF signals.
 7. The outphasing calibration method according to claim 6, further comprising amplifying, by the circuitry, at least the second plurality of phase-shifted RF signals to generate at least a second plurality of amplified RF signals.
 8. The outphasing calibration method according to claim 7, wherein the transmitter antenna is configured to transmit a first output RF signal and a second output RF signal to an outphasing RF receiver, and wherein the transmitted first output RF signal is based on a first combination of the first plurality of amplified RF signals and the transmitted second output RF signal is based on a second combination of the second plurality of amplified RF signals.
 9. The outphasing calibration method according to claim 8, further comprising storing, by the circuitry, the detected differences of the first plurality of signal characteristics of the first plurality of amplified RF signals in a memory device.
 10. The outphasing calibration method according to claim 9, further comprising: retrieving, by the circuitry, the stored detected differences of the first plurality of signal characteristics of the first plurality of amplified RF signals from the memory device, and controlling, by the circuitry, at least one signal characteristic of each of the second plurality of amplified RF signals based on the retrieved detected differences.
 11. The outphasing calibration method according to claim 7, wherein the first plurality of signal characteristics and the second plurality of signal characteristics comprise at least a phase value, a gain value, an outphasing value, or a voltage value corresponding to each of the first plurality of amplified RF signals and the second plurality of amplified RF signals.
 12. An outphasing calibration radio frequency (RF) transmitter, comprising: a first load impedance coupled across a first power amplifier (PA) and a second load impedance coupled across a second PA, wherein the first load impedance is configured to receive a first current that is generated based on a first voltage drop across the first PA, and wherein the second load impedance is configured to receive a second current that is generated based on a second voltage drop across the second PA; a first phase detector coupled across the first load impedance and a second phase detector coupled across the second load impedance, wherein the first phase detector and the second phase detector are configured to detect differences of a first signal characteristic of at least one signal characteristic of a first plurality of amplified RF signals across the first load impedance and the second load impedance; a transmitter signal strength indicator (TSSI) circuit coupled across a transmitter antenna and the first PA, wherein the TSSI circuit is configured to detect differences of a second signal characteristic of the at least one signal characteristic of the first plurality of amplified RF signals across the transmitter antenna; and a signal processing circuit and a plurality of phase shifters, wherein the signal processing circuit and the plurality of phase shifters are coupled to the TSSI circuit, the first phase detector, and the second phase detector, wherein the signal processing circuit and the plurality of phase shifters are configured to perform a first calibration and a second calibration of the at least one signal characteristic of a second plurality of amplified RF signals, wherein the first calibration and the second calibration are based on a controlled generation of a first plurality of constant-envelope signals, wherein the first plurality of constant-envelope signals are generated on a plurality of transmission paths, and wherein the controlled generation of the first plurality of constant-envelope signals is based on the detected differences of the first signal characteristic and the second signal characteristic.
 13. The outphasing calibration RF transmitter according to claim 12, wherein the signal processing circuit is further configured to: generate the first plurality of constant-envelope signals based on a first out-phasing of a first modulated input signal, generate a second plurality of constant-envelope signals based on a second out-phasing of a second modulated input signal, and wherein the first plurality of constant-envelope signals and the second plurality of constant-envelope signals comprises digital signals with constant amplitudes.
 14. The outphasing calibration RF transmitter according to claim 13, wherein the signal processing circuit is coupled to a digital-to-analog converter, and wherein the digital-to-analog converter is configured to: convert the first plurality of constant-envelope signals into a first plurality of constant-envelope analog signals, and convert the second plurality of constant-envelope signals into a second plurality of constant-envelope analog signals.
 15. The outphasing calibration RF transmitter according to claim 14, wherein the signal processing circuit is coupled to a frequency mixer, and wherein the frequency mixer is configured to: up-convert the first plurality of constant-envelope analog signals into a first plurality of constant-envelope RF signals, up-convert the second plurality of constant-envelope analog signals into a second plurality of constant-envelope RF signals, and wherein the first plurality of RF signals and the second plurality of RF signals are up-converted based on local oscillations.
 16. The outphasing calibration RF transmitter according to claim 12, wherein at least one phase shifter of the plurality of phase shifters is configured to phase-shift each of the second plurality of amplified RF signals with a defined value to generate a second plurality of phase-shifted RF signals.
 17. The outphasing calibration RF transmitter according to claim 16, wherein the first PA and the second PA are configured to amplify at least the second plurality of phase-shifted RF signals to generate at least the second plurality of amplified RF signals.
 18. The outphasing calibration RF transmitter according to claim 12, wherein the transmitter antenna is configured to transmit a first output RF signal and a second output RF signal to an outphasing RF receiver, wherein the transmitted first output RF signal is based on a first combination of the first plurality of amplified RF signals and the transmitted second output RF signal is based on a second combination of the second plurality of amplified RF signals.
 19. A non-transitory computer-readable medium having stored thereon, computer executable instruction that when executed by a computer, cause the computer to execute instructions, the instructions comprising: in an outphasing radio frequency (RF) transmitter: detecting differences of a first plurality of signal characteristics of a first plurality of amplified RF signals across at least a transmitter antenna or a plurality of load impedances, wherein the first plurality of amplified RF signals correspond to a first plurality of constant-envelope signals; controlling generation of a second plurality of constant-envelope signals, wherein the second plurality of constant-envelope signals are generated on a plurality of transmission paths, wherein the second plurality of constant-envelope signals are generated based on the detected differences of the first plurality of signal characteristics; and at least one of first calibrating or second calibrating a second plurality of signal characteristics of the second plurality of constant-envelope signals, wherein the first calibrating and the second calibrating are based on the controlled generation of the second plurality of constant-envelope signals.
 20. The non-transitory computer-readable medium according to claim 19, wherein the instructions further comprises: generating the first plurality of constant-envelope signals based on a first out-phasing of a first modulated input signal, and generating the second plurality of constant-envelope signals based on a second out-phasing of a second modulated input signal, wherein the first plurality of constant-envelope signals and the second plurality of constant-envelope signals comprises digital signals with constant amplitudes. 